Telephone-transmitter.



N0. 833,449. PATENTED OCT. 16, 1906.

S. A. DUVALL.

TELEPHONE TRANSMITTER.

APPLIOATION FILED HAR. 5, 190s.

Y'UNITED STATES,

PATENT oEEroE.

` TELEPHONE-TR'ANSNIITTER.

Specification of Letters-Patent.

1 atentedOct.` 16, 1906.

. Application led March 5, 1903- Serial No. 146,310.

v and useful Improvement in Telephone-Transmitters, of which the'following is a specification.

My invention relates to microphone orbattery transmitters of. the granular type, and has for its object the production of an instrument of this kind which shall be sensitive but certain in its action, which can be readily adjusted at all times without dismantling, and which will retain its adjustment under trying conditions and with severe usage.` To this end I adopt the principles and embody them in a manner which will presently be described,

and pointed out in the appended claims.

My inventioncomprises an arrangement wherein the microphone-button is made as a complete unit, -thus gaining all the advantages of the solid-back instrument, but is provided with an adjustment for the electrodes which obviates' the necessityfor absolute uniformity in the parts or their assembling, thus doing away wi h the expert labor and producing an article of a purely commercial type. In this arrangement instead of a mica auxiliary diaphragm I employ a diaphragm of metal, preferably reiined aluminium, which after repeatedexperiments I iind gives a better results for my purposes than any other metal that is commercially available. rI`he only material heretofore used in this manner has been mica, and while by expert selection sheets of this material of fairlyuniform thickness can be obtained it is impossible to get perfect uniformity in the lphysical properties. Moreover, slight variations in thickness seein to produce quite a difference in the tone of the instrument, so that it is necessary to discard much material to obtain the little that is of use. On the other hand, in aluminium I have a material that presents two striking advantages for this purpose-lightness of mass to be moved and perfect and uniform resilience. I commonly employ cold-rolled sheet-aluminium one-thousandth of an inch thick to micrometer gage. Being of metal, the diaphragm is impervious to moisture, is not injured by changes in temperature, and gives very uniform results in use. Owing to its lightness, as well as its small diameter and mass, it has a very high natural period entirely removed from the ordinarynrange of voice vibrations, which, therefore, it does not alter, but reproduces with great fidelity.

' My invention is illustrated in the accompanying drawings, wherein- Figure 1 is a cross-sectiontakenalong-the middle line of the bridge of a -transmitter embodying my improvements, while Fig. 2 is a detail view of the vparts of the transmitterbutton separated from each other.

Referring to Fig. 1, A is the front plate of the transmitter, having a `central opening a screw-threaded, as usual, for the reception of the hard-rubber mouthpiece a 4 Extending around the circumference of the rear -face of the front plate is the annularrflange a2, which has three functions. It forms a yrecess on the inside for the diaphragm'to lie in, it forms a shoulder on the outside for the shell S to be screwed to, and it furnishes a face for the attachment of the bridge B. The diaphragm D has its edge surrounded by a softrubber gasket d, which insulates it from the front plate, and it is held in position by clamping and damping springs d', all in the usual manner. The bridge B has a central boss b and is provided with an axial opening b for the reception of thefstemy of the button.

'The entire instrument when assembled and adjusted, so far as its operative parts are concerned, is supported upon the front plate A and as a last step in the assembling is inclosed within the metal shell S, secured to the flange a2 in any suitable manner. The shell has a Hat base s, secured by screws s or otherwise to the end of the hollow arm X, land is centrally perforated, as at s2, to permit the passage of the circuit-wires from the diaphragm and the bridge connection, respectively, into the hollow arm, as shown.

The transmitter-button has for its essential parts the following7 which are separately shown in Fig. 2 and assembled in Figli: the metal cup or pill-box C, having a hollow stem c provided with internal screw-thread c in the stem and external screw-thread c2 on its front edge; rear electrode E, consisting of a metal disk e, with a carbon face e and stem e2 fitted to the hollow stem of the cup C and screw-threaded to work therein, being also rovided with an end slot e3 or the purpose of making and securing the adjustment; front electrode F consisting o a metal disk f, with a carbon face f and cen- ICO tral stem f2, screw-threaded to receive the lock-nutsf3, by which it is secured to the diaphragm D; aluminium auxiliary diaphragm G, secured to the back of the front electrodedisk f by means of the screw-threaded disknut g; interior ring bushing or lining I-I, which may be of rubber, compressed mica, or other suitable material and is fitted to the inside of the cup C, having a forward shoulro der h, upon which the auxiliary diaphragm G rests; locking-ring c4, which, with an interposed insulating-gasket 7L', holds down the auxiliary diaphragm upon the shoulder h and which is screwed to the cup C by means of its r 5 threads c5 engaging with the threads c2.

It will be observed that I make the front electrode smaller than the rear electrode in order to form the usual expansion-chamber for the granular carbon when it becomes zo heated.

In assembling this instrument the steps are as follows: The microphonic button, consisting of the cup C and the other parts shown in Fig. 2, is first assembled as a unit,

containing the proper quantity of granular material I. The diaphragm is then secured upon the front plate, and the stem f2 of the front electrode is secured thereto by the nuts f3, the bridge B being at the same time 3 o slipped over the stem c and screwed to the annular flange a2. The button is now adjusted roughly by means of the stem c, so that the auxiliary diaphragm G is under no tension, but is in y a natural unbuckled condition,

3 5 when the stem c is rigidly secured by the setscrew b2. Up to this point no skilled labor is required, except that accuracy in assembling the button is somewhat necessary; but as this work is usually done by girls who are deft 4o with their fingers it is capable of swift and easy performance. The instrument being suitably connected up is finely and finally adj usted by means of a screw-driver inserted in the slot e3, this adjustment being rendered 4 5 permanent by means of the lock-nuts e4. This work of adjustment should be done by one person specially trained, and the final results obtained in this way are astonishing, even to those who have been accustomed to 5o consider the solid-back transmitter a sensitive and powerful instrument. I ascribe these results to my use of a very thin metal auxiliary diaphragm, preferably of aluminium, and an adjustable rear electrode. As a 5 5 general rule I also make the body and stem of the front electrode, together with the clamping-nut g, of aluminium, and I consider this also an important part of the invention, although I do not wish to be limited to the use 6o of this metal exclusively, as some other invention in its broadest aspect comprehend-- ing the combination I have indicated.

Having thus described my invention, what I claim, and desire to secure by Letters Patent of the United States, is`

1. In a telephone-transmitter, the combination with a ca'sing, of a frame mounted in said casing, a cup containing a resistancechamber adjustably mounted in said frame, an electrode adjustably mounted in said cup,

insulating means within the cup, an auxiliary diaphragm mounted on said insulating means, another electrode mounted on said diaphragm, a main diaphragm connected to said last-named electrode, and granular material between said electrodes.

2. In a telephone-transmitter, the combination with a casing, of a frame mounted in said casing, a cup containing a resistancechamber, a shank connected to said cup and adjustably mounted in said frame, an electrode in said cup provided with a shaft passing through an aperture in said shank and adjustably connected thereto, insulating means in said cup, an auxiliary diaphragm carried by said insulating means, an electrode supported on said auxiliary diaphragm, a shaft on said electrode, a main diaphragm connected to said shaft so that when actuated it will convey the vibrations to said auxiliary diaphragm, and granular material between the electrodes in the cup.

3. A resistance button for telephonetransmitters comprising a supporting-shank and cup integral therewith, an insulatingring within said cup and provided with a threaded shoulder, a supplemental diaphragm resting upon said insulating-ring,

means for clamping the diaphragm in position upon the insulating-ring, said means also connected to the cup, an electrode supported by said supplemental diaphragm, and granular material in the cup.

In Witness whereof I have hereunto set my hand 6th day of February, A. D. 1903, in the presence of two subscribing witnesses.

STANLEY A. DUVALL Witnesses:

CORINNE BENTLEY,l G. L. KERSTETTER. 

